In a control system haying a spring mass system such as an electromagnetic valve, it is hard to sufficiently secure robustness with respect to a disturbance, a characteristic change of the electromagnetic valve or the like, in accordance with a control method such as a PID control or the like. Accordingly, there has been considered such a control as to converge a state quantity of a controlled object on a switching hyperplane expressed by a desirably designed linear function in accordance with a high gain control by applying a sliding mode control to the control system mentioned above, and bind it on the switching hyperplane. In the sliding mode control apparatus mentioned above, there has been proposed a technique which can further satisfy a plurality of request elements without contradiction (for example, Japanese Laid-Open Patent Publication No. 2003-202901).
However, the Japanese Laid-Open Patent Publication No. 2003-202901 does not cope with a case that an external force caused by a cylinder internal pressure of an internal combustion engine or the like is applied as a disturbance, or a case that a neutral point of a spring of an electromagnetic valve is changed due to a change with time, and there is a risk that the operation is destabilized on the basis of an operating state of the internal combustion engine or the change with time. The destabilization mentioned above may be caused by a machine error generated at a time of manufacturing the controlled object such as the electromagnetic valve or the like.